A transparent liquid crystal device or transflective liquid crystal device partially uses outside light, but mainly uses a light source which is mounted in the device. As this light source, a backlight is used.
To supply the light from the back of liquid crystal cells, this backlight is disposed on the back of the liquid crystal cells in a view from the display side of the device. This backlight is mainly constructed of light guide plates whose main surface is disposed substantially parallel to the surface on the back side of the liquid crystal cells and an edge light (side light) disposed on the edge surface side of the light guide plate for introducing light into this edge surface. Furthermore, a reflective sheet is disposed opposite the liquid crystal cell side of the light guide plate.
In such a structure, the light from the edge light propagates inside the light guide plate, and is reflected on light-emitting means provided on the light guide plate and on a reflective sheet disposed outside the light guide plate, and is redirected to the liquid crystal cells, and is then introduced into the liquid crystal cells.
Mobile phones having two displays are becoming widespread in recent years. In a case that the light is supplied to these two displays, a backlight is provided for each display.
FIG. 1 shows a structure of a conventional backlight having two displays. In the figure, reference numerals 101, 102 denote backlights for a main display (relatively large display) which supply the light in the direction indicated by arrow A. In the figure, reference numerals 107, 108 denote backlights for a sub-display (relatively small display) which supply the light in the direction indicated by arrow B.
The backlight for the main display is mainly constructed of a light guide plate 101 and an edge light (side light) disposed on one edge surface side of this light guide plate 101. As this edge light, an LED is normally used. A diffusion sheet 103 for diffusing the light emitted from the light guide plate 101 is disposed on one main surface (light-emitting surface) of the light guide plate 101.
On the diffusion sheet 103, an isotropic prism sheet 104 is disposed. As this isotropic prism sheet 104, for example, BEF (manufactured by 3M Worldwide Japan, trade name), etc., can be used. A plurality of prism-shaped protrusions are formed on the surface of this isotropic prism sheet 104 to condense the light in the direction perpendicular to the ridge lines of the protrusions.
An isotropic prism sheet 105 is disposed on the isotropic prism sheet 104. As this isotropic prism sheet 105, for example, BEF (trade name), etc., can be used. A plurality of prism-shaped protrusions are formed on the surface of this isotropic prism sheet 105 and the ridge lines of the protrusions are disposed perpendicular to the ridge lines of the protrusions of the isotropic prism sheet 104. Furthermore, this isotropic prism sheet 105 condenses the light in the direction perpendicular to the ridge lines of the protrusions.
The backlight for the sub-display is mainly constructed of a light guide plate 107 and an edge light 108 disposed on one edge surface side of this light guide plate 107. As this edge light, an LED is normally used. A diffusion sheet 109 for diffusing the light emitted from the light guide plate 107 is disposed on one main surface (light-emitting surface side) of the light guide plate 107.
An isotropic prism sheet 110 is disposed on the diffusion sheet 109. As this isotropic prism sheet 110, BEF (trade name), etc., can be used. A plurality of prism-shaped protrusions are formed on the surface of this isotropic prism sheet 110 to condense the light in the direction perpendicular to the ridge lines of the protrusions.
An isotropic prism sheet 111 is disposed on the isotropic prism sheet 110. As this isotropic prism sheet 111, BEF (trade name), etc., can be used. A plurality of prism-shaped protrusions are formed on the surface of this isotropic prism sheet 111 and the ridge lines of the protrusions are disposed perpendicular to the ridge lines of the protrusions of the isotropic prism sheet 110. Furthermore, this isotropic prism sheet 111 condenses the light in the direction perpendicular to the ridge lines of the protrusions.
A reflective plate 106 is disposed between the other main surface of the light guide plate 101 and the other main surface of the light guide plate 107. This reflective plate 106 prevents the light of the backlight on the main display side from being supplied to the sub-display side and on the contrary, prevents the light of the backlight on the sub-display side from being supplied to the main display side.
In the above described structure, it is necessary to provide the backlights 101, 102 to illuminate the main display, and the backlights 107, 108 to illuminate the sub-display respectively, which results in an increased number of parts and an increased thickness of the device as a whole.